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Honors student James Holmes, 24, studied neuroscience at the University of Colorado's medical school but was in the process of withdrawing from graduate school. Neighbors called him a loner; Holmes wrote on an apartment application that he is "quiet and easy going." He is suspected of carrying out a killing spree in an Aurora movie theater, but Holmes' criminal history included nothing more than a single speeding ticket, NBC 6's Keith Jones reports. "As you can imagine, the Holmes family is very upset about all of this," said San Diego Police Department Lt. Andra Brown. (Published Friday, July 20, 2012)

Updated at 1:18 PM EDT on Tuesday, Sep 25, 2012

A graduate student masquerading as Batman's nemesis the Joker opened fire in a Colorado movie theater during a midnight screening of "The Dark Knight Rises" killing 12 and injuring another 58 early Friday, authorities said.

James Holmes -- who was wearing body armor and a gas mask when taken into custody outside the theater in Aurora, Colo. -- told police he was the Joker and warned them that his nearby apartment was rigged with explosives, but said little else before refusing to cooperate, NBC News reported.

Aurora, Colo., Cinema Rampage Remembered

Authorities apprehended Holmes, 24, whose hair was dyed red or orange, in the parking lot of the theater moments after the massacre. Cops found two 40-caliber Glock handguns, a Remington 870 single-barrel shotgun and a Smith and Wesson AR-15 assault-style rifle at the scene, which they confiscated along with his white Hyundai, Aurora Police Chief Dan Oates said during an afternoon press conference in the Denver suburb. The weapons, Oates later said, had been purchased legally.

"It was just total chaos," witness Ben Fernandez told 9 News. "There were people running, screaming 'my friend just got shot, my sister just got shot' everywhere you turned. People were just in a complete panic."

Law enforcement officials descended upon Holmes' apartment, located several miles from the movie theater, and found it loaded with trip wires, bottles of liquid, containers of ammunition, fireworks and powder.

"I personally have never seen anything like what the pictures showed us," Oates said at an evening news conference. "It's a very vexing problem," trying to figure out how to safely enter the apartment.

Police, who decided to hold off on entering the apartment until additional resources were flown in Saturday, evacuated five apartment buildings in the area and moved residents to a local high school, where they'll stay overnight.

Oates nearly broke down during the final press conference of the day when responding to a question about how the police force was faring.

"The cops went through a lot," he said. When everything settles down, he added, the focus would shift to dealing with "our own trauma."

Before moving to Aurora, Holmes was a top-notch college student who seemed to lose his way after leaving home in San Diego to pursue a PhD, friends and associates say.

Holmes ended up at the University of Colorado Medical School’s campus in Aurora, where he reportedly fell behind on his work in recent months and was planning to drop out. In class, he became “strangely quiet” and seemed “socially off,” a faculty member told the Washington Post. He also began buying the guns that he would allegedly bring into a crowded Aurora theater before calmly opening fire during a midnight screening of the latest Batman movie.

When news of the mass shooting reached Holmes’ hometown, neighbors and former classmates were aghast.

“He was shy and a little quiet, but he was never aggressive or mean,” Sumit Shah, who attended Westview High School with Holmes, told NBC San Diego.

“It’s kind of weird to see him go from the guy I knew to somebody who would kill 12 people and counting.”

Holmes graduated from Westview High School in San Diego in 2006 and back then went by the name Jimmy, classmate Sumit Shah told NBC 4 New York.

“I knew him pretty well, we were friendly,” Shah said. “He was pretty shy, but once he got comfortable with you he was the funniest, smartest guy… He always had something witty to say.”

Shah said he was shocked that his former classmate was "The Dark Knight" shooting suspect.

“The guy I knew in high school, I don’t understand how that could be the same guy,” he said.

Holmes’ uncle, also named James Holmes, said his nephew was a “nerd” and an “unassuming kid.”

After high school, Holmes attended the University of California at Riverside, where he majored in neuroscience and graduated with honors in 2010. But when he returned home, had had trouble finding work, neighbors told Rancho Bernardo Patch.

In Aurora, he lived in an apartment building reserved for students and faulty of the medical school. On his rental application he reportedly described himself as “quiet and easy going,” the Denver Post reported. A neighbor told the paper that Holmes kept to himself.

Benjamin Fernandez, 30, told the Denver Post that he heard a series of explosions. He said that people ran from the theater and there were gunshots as police shouted "get down!"

Fernandez said he saw people falling, including one young girl.

Jordan told the paper that one girl was struck in cheek, others in stomach including a girl who looked to be around 9-years-old.

Jordan said it sounded like firecrackers until someone ran into Theater 8 yelling "they're shooting out here!"

Hayden Miller told KUSA-TV that he heard several shots.

"Like little explosions going on and shortly after that we heard people screaming," he told the station.

Hayden said at first he thought it was part of a louder movie next door. But then he saw "people hunched over leaving theater."

Police, ambulances and emergency crews swarmed on the scene after frantic calls started flooding the 911 switchboard, officials said.

Officers came running in and telling people to leave the theater, Salina Jordan told the Denver Post. She said some police were carrying and dragging bodies.

There was no immediate word on the suspect's motive. The Pentagon told the AP some members of the military were either killed or wounded in the attack. An FBI official told NBC News that there were no indications of a connection to international terrorism.

Oates said police also checked for explosives in the parking lot and at the Century 16 theater and secured those areas.

Victims being treated at area hospitals included a 6-year-old and a 4-month-old. The infant was later released from a hospital, NBC News reported.

“Today is a moment to grieve and to remember, to reach out and help, to appreciate our blessings in life,” Romney said later at a campaign appearance in New Hampshire.

Warner Bros., the studio behind "The Dark Knight Rises," said in a statement the company and filmmakers were "deeply saddened to learn about this shocking incident. We extend our sincere sympathies to the families and loved ones of the victims at this tragic time."

Tim Warner, the president and CEO of Cinemark, which owns the Aurora movie theater where the shooting took place, said his prayers were with the victims and their families.

“This is just a huge, huge tragedy. For me personally, this is very heartbreaking. I just feel devastated,” he told NBC DFW.

AMC theaters said in a statement their thoughts were with victims and their families.

“For the safety and security of our guests and associates, we are actively working with local law enforcement in communities throughout the nation and under the circumstances we are reaching out to all of our theaters to review our safety and security procedures,” AMC said in a statement.

Aurora's police chief at first said 10 victims died at the theater and four at area hospitals, but later revised the death toll down to 12.

Aurora is on Denver's east side and is Colorado's third-largest city with 327,000 residents. It is home to a large Defense Department satellite intelligence operation at Buckley Air Force Base, as well as The Children's Hospital, the University of Colorado Hospital and a future Veterans Affairs hospital.

“We’ve taken a blow today but we will get back on our feet and we will move ahead,” Aurora Mayor Steve Horan told reporters.